Configurable download address

[luoye-fe]

Is your feature request related to a problem? Please describe. You know, downloading github assets in mainland China is particularly slow~

Describe the solution you'd like Maybe, allow to specify local model dir? Such as:

EfficientNetCheckPointFactory.create(EfficientNetCheckPoint.B7, {
  localModelRootDir: path.join(__dirname, 'tf-model'),
});

Describe alternatives you've considered

Additional context Add any other context or screenshots about the feature request here.

[ntedgi]

should be enabled as part of #6

[luoye-fe]

28